In the area of technology which relates to printing, such as facsimile, xerography, magnetography, etc., a standard procedure is one in which a uniform coating such as ink or toner is selectively applied on a recording medium that is adjacent to a recording head via a toner applicator such as a magnetic brush. The recording head in one form of printing system would be a write head which is capable of providing magnetic latent images of symbols, such as alpha-numeric characters, on a recording medium in a straight line configuration. The recording medium may be an endless loop of magnetic tape moving between the write head and a magnetic brush, and the ink or toner on the brush will be magnetically attracted to the recording medium in response to the magnetic output of the write head. In most xerographic systems the toner applicator is in direct contact with a photoreceptor surface to selectively coat the surface with toner. Depending on the system employed, the toner applicator may be in the form of a magnetic brush, fur brush, roller, etc. For further details of such a magnetographic system, reference can be made to U.S. Pat. No. 3,945,343 dated Mar. 23, 1976 and assigned to the common assignee.
Regardless of the form of the components in a given printing system, some parallelism must be achieved between the respective parts to insure that a uniform thickness of ink or toner is applied over the contact length of the parts, adjacent to, or on, a given receptor surface by the toner applicator.
Even though this condition is common in both xerographic and magnetographic systems, it is less of a problem in a xerographic environment due to the relatively larger forces involved in the recording method.
In a magnetographic system the attractive forces between the recording medium and the toner on the magnetic brush are much smaller and parallelism between the respective parts becomes critical.
A magnetographic system may employ a magnetic rotating brush in a toner reservoir for applying toner particles to a moving surface of a recording medium. As the brush is rotated a uniform layer of toner selectively covers the moving surface of a recording medium where latent images have been recorded. If the surface of the recording medium is not parallel to the axis of rotation of the magnetic brush, a print intensity gradient will appear on the recording medium, such as magnetic recording tape.
The gradient is due to the fact that toner is attracted by both the magnetic field of the brush and the field of the magnetic latent images on the recording medium. The recording medium passes through the mantle of toner particles surrounding the magnetic brush. The magnetic portions of the recording medium closest to the axis of rotation of the brush will receive proportionately lesser amounts of magnetic ink or toner than those magnetic portions of the recording medium more remote from the axis of rotation because the magnetic attractive force of the brush closest to the brush axis is stronger and impedes transfer of toner to the magnetic latent images on the tape.
While the horizontal alignment accuracy of the brush along the magnetic tape surface can be readily obtained, the problem of vertical alignment accuracy of the axis of rotation of the brush in parallel with the recording medium has not been easy to solve. Due to machine design limitations any adjustment mechanism incorporated into the machine should be compact, uncomplicated, simple to manipulate and accurate.
To solve this problem it has been necessary to develop a linear vertical axial adjustment mechanism with no horizontal component, which will insure parallelism between the axis of rotation of the magnetic brush and the recording medium. Some of the specific solutions which were investigated are: a screw jack and slider mechanism, which was subject to backlash and found to be too complicated for the intended purpose; and eccentric washer shaped, continuously rotatable discs, which had unacceptable horizontal movement for every vertical adjustment.
A structure was needed to produce an incremental, linear, vertical, axial adjustment without any horizontal component, which was simple to operate, compact, reproducible, reliable, and accurate while being of relatively low cost.